LILY PENG: Hi everybody.

My name is Lily Peng.

I'm a physician by training and I work on the Google medical--

well, Google AI health-care team.

I am a product manager.

And today we're going to talk to you about a couple of projects

that we have been working on in our group.

So first off, I think you'll get a lot of this,

so I'm not going to go over this too much.

But because we apply deep learning

to medical information, I kind of wanted

to just define a few terms that get used quite a bit

but are somewhat poorly defined.

So first off, artificial intelligence-- this

is a pretty broad term and it encompasses that grand project

to build a nonhuman intelligence.

Machine learning is a particular type

of artificial intelligence, I suppose,

that teaches machines to be smarter.

And deep learning is a particular type

of machine learning which you guys have probably

heard about quite a bit and will hear about quite a bit more.

So first of all, what is deep learning?

So it's a modern reincarnation of artificial neural networks,

which actually was invented in the 1960s.

It's a collection of simple trainable units, organized

in layers.

And they work together to solve or model complicated tasks.

So in general, with smaller data sets and limited compute,

which is what we had in the 1980s and '90s,

other approaches generally work better.

But with larger data sets and larger model sizes

and more compute power, we find that neural networks

work much better.

So there's actually just two takeaways

that I want you guys to get from this slide.

One is that deep learning trains algorithms

that are very accurate when given enough data.

And two, that deep learning can do this

without feature engineering.

And that means without explicitly writing the rules.

So what do I mean by that?

Well in traditional computer vision,

we spend a lot of time writing the rules

that a machine should follow to make a certain prediction task.

In convolutional neural networks,

we actually spend very little time in feature

engineering and writing these rules.

Most of the time we spend in data preparation

and numerical optimization and model architecture.

So I get this question quite a bit.

And the question is, how much data is enough data

for a deep neural network?

Well in general, more is better.

But there are diminishing returns beyond a certain point.

And a general rule of thumb is that we

like to have about 5,000 positives per class.

But the key thing is good and relevant data--

so garbage in, garbage out.

The model will predict very well what you ask it to predict.

So when you think about where machine learning,

and especially deep learning, can make the biggest impact,

it's really in places where there's

lots of data to look through.

One of our directors, Greg Corrado, puts it best.

Deep learning is really good for tasks that you've done 10,000

times, and on the 10,001st time, you're just sick of it and you

don't want to do it anymore.

So this is really great for health care in screening

applications where you see a lot of patients

that are potentially normal.

It's also great where expertise is limited.

So here on the right you see a graph

of the shortage of radiologists kind of worldwide.

And this is also true for other medical specialties,

but radiologists are sort of here.

And we basically see a worldwide shortage of medical expertise.

So one of the screening applications

that our group has worked on is with diabetic retinopathy.

We call it DR because it's easier

to say than diabetic retinopathy.

And it's the fastest growing cause of preventable blindness.

All 450 million people with diabetes are at risk and need

to be screened once a year.

This is done by taking a picture of the back

of the eye with a special camera, as you see here.

And the picture looks a little bit like that.

And so what a doctor does when they get an image like this

is they grade it on a scale of one to five from no disease,

so healthy, to proliferate disease,

which is the end stage.

And when they do grading, they look for sometimes very subtle

findings, little things called micro aneurysms

that are outpouchings in the blood vessels of the eye.

And that indicates how bad your diabetes

is affecting your vision.

So unfortunately in many parts of the world,

there are just not enough eye doctors to do this task.

So with one of our partners in India,

or actually a couple of our partners in India,

there is a shortage of 127,000 eye doctors in the nation.

And as a result, about 45% of patients

suffer some sort of vision loss before the disease is detected.

Now as you recall, I said that this disease

was completely preventable.

So again, this is something that should not be happening.

So what we decided to do was we partnered

with a couple of hospitals in India,

as well as a screening provider in the US.

And we got about 130,000 images for this first go around.

We hired 54 ophthalmologists and built a labeling tool.

And then the 54 ophthalmologists actually

graded these images on this scale,

from no DR to proliferative.

The interesting thing was that there was actually

a little bit of variability in how doctors call the images.

And so we actually got about 880,000 diagnoses in all.

And with this labelled data set, we put it through a fairly well

known convolutional neural net.

This is called Inception.

I think lot of you guys may be familiar with it.

It's generally used to classify cats and dogs for our photo app

or for some other search apps.

And we just repurposed it to do fundus images.

So the other thing that we learned

while we were doing this work was

that while it was really useful to have

this five-point diagnosis, it was also

incredibly useful to give doctors

feedback on housekeeping predictions like image quality,

whether this is a left or right eye,

or which part of the retina this is.

So we added that to the network as well.

So how well does it do?

So this is the first version of our model

that we published in a medical journal in 2016 I believe.

And right here on the left is a chart

of the performance of the model in aggregate

over about 10,000 images.

Sensitivity is on the y-axis, and then 1 minus specificity

is on the x-axis.

So sensitivity is a percentage of the time when

a patient has a disease and you've

got that right, when the model was calling the disease.

And then specificity is the proportion

of patients that don't have the disease that the model

or the doctor got right.

And you can see you want something

with high sensitivity and high specificity.

And so up and to the right--

or up and to the left is good.

And you can see here on the chart

that the little dots are the doctors that

were grading the same set.

So we get pretty close to the doctor.

And these are board-certified US physicians.

And these are ophthalmologists, general ophthalmologists

by training.

In fact if you look at the F score, which

is a combined measure of both sensitivity and specificity,

we're just a little better than the median ophthalmologist

in this particular study.

So since then we've improved the model.

So last year about December 2016 we were sort of on par

with generalists.

And then this year--

this is a new paper that we published--

we actually used retinal specialists

to grade the images.

So they're specialists.

We also had them argue when they disagreed

a